Synthesis and properties of conjugated oligomers containing fluorene, fluorenone, thiophene and cyclopentadithiophenone units

Conjugated oligomers based on fluorene, fluorenone and thiophene derivatives have been prepared by parallel synthesis using the Suzuki cross-coupling reaction. These oligomers can be used as models of the corresponding fluorene copolymers and their structures were correlated with the observed optical and electrochemical behaviour. The long wavelength absorption bands observed for oligomers that contain fluorenone or cyclopentadithiophene units were assigned to an allowed π–π* transition associated with the carbonyl containing monomer unit. In addition the photoluminescence efficiency and the concentration dependence of the long wavelength emission band (>525 nm) for these materials strongly suggests that it can be attributed to emission involving fluorenone-based excimers.